Seasonal changes in egg mass and timing of laying in the Madagascar Paradise Flycatcher, Terpsiphone mutata

Abstract

Variations in egg mass and egg-laying date for the Madagascar Paradise Flycatcher, Terpsiphone mutata, were studied from 1996 to 1998 in deciduous dry forest of the Ampijoroa Forest Station, northwestern Madagascar. There was a significant seasonal change in egg mass. An egg laid in the middle or late breeding season was heavier than one laid by the same female in the early breeding season. Egg mass was not correlated with temperature or precipitation, but was positively correlated with the abundance of insects. This suggests that egg mass appears to be constrained by insect supply, resulting in a seasonal change in egg mass. During the study period, variation in egg mass did not seriously affect breeding success, though it is possible that high predation masked the real effect. Earlier laying may be advantageous for nesting pairs, because the young are then in the nest when food is most abundant; it also allows them sufficient time to re-nest if their first nest suffers predation. Heavier eggs were found to lead to heavier nestlings, which may be advantageous in the late breeding season if insects are scarce and parents are unable to catch enough food. Heavier body mass might therefore be important for later nestlings' growth and survival.